Today, we are continuing our Gardening Q & A series, answering your most-asked questions about anything garden-related.

If you missed that article about raised bed soil fertility, you can catch up here.

Two weeks ago, the question we addressed in our first Q&A was how to improve soil, especially in raised beds or large containers. Two questions were presented — how to get freshly added soil optimal for newly raised beds, and what to do with soil that produced poor quality vegetables.

Several readers had excellent thoughts and observations, so we decided to continue the conversation for another session, as this topic is essential for any gardener — how do we create and maintain healthy, fertile, diverse soil in our gardens, and what should we be aware of and avoid?

Now, our reader’s responses, thoughts, and shared experiences.

One concern most often voiced was, “I’m wondering about the soil issue in this first question – where did the compost come from? Was there any possibility of it having been contaminated with herbicides? I’ve seen reviews of commercial compost/manures where the users recounted results like that and surmised that their compost wasn’t organic, as advertised. I don’t know if there’s any way to test soil for that kind of thing.”

Unfortunately, widely available commercial compost isn’t always made with the same care you would use in your backyard. Raw inputs — called feedstocks — aren’t always available from the same suppliers, such as landscaping companies, tree trimming companies, or mowing and cleanup companies. When the compost company runs out of suppliers, they will sometimes turn to less desirable feedstock laced with herbicides, pesticides, fungicides, or any other soil organism killers. Often, this damages your garden’s compost, with almost no way for you to know beforehand.

Two specific instances illustrate how this has happened to our customers in the past.

It was late spring, about a decade ago, when we started receiving frantic phone calls about how seedlings — primarily tomatoes and peppers — died within hours after being transplanted. A pattern appeared after talking with several customers and asking specific questions about what potting or garden soil they used. It pointed to one brand of potting soil, composted from reclaimed biosolids, also known as sewage.

In this following example, it took longer to discover why plants and seedlings were dying after transplanting, and seeds never germinated, simply because there were only a couple of customers in one geographic area.

It started with a call from a customer asking why her seedlings and plants were dying after being transplanted, and her seeds never came up.

We asked the usual questions about soil moisture, temperature, and germination time but found nothing unusual. Further conversations revealed newly added mushroom compost, bought from a local hardware garden store with an excellent reputation in the area. I assumed (!) that all mushroom compost was the same, made the same way from recycled mushroom-growing medium or finely shredded wood chips.

After asking the mushroom grower, the hardware store discovered that the growing media consisted of finely shredded wood chips loaded with salt to prevent anything other than mushrooms from growing.

These responses and examples show why gardening or potting soil is not a commodity and why you need to trust where it comes from.

One tool that makes things more accessible is the OMRI label on a product, indicating they have inspected and accepted it for organic production. OMRI stands for the Organic Materials Review Institute, a non-profit organization based in Oregon. Look for their label on a bag or product to know you are buying top-shelf products.

A knowledgeable, experienced supplier is essential, whether local to you or not — ask questions about the product and source materials so you know what you are buying and putting into your garden soil.